Water on the knee

Water on the knee is a general term for excess fluid accumulation in or around your knee joint. Your doctor may refer to this condition as an effusion (uh-FU-zhun) in your knee joint.

Water on the knee may be the result of trauma, overuse injuries, or an underlying disease or condition. To determine the cause of water on the knee, your doctor may need to obtain a sample of the fluid to test for infection, disease or injury.

Removing some of the fluid also helps reduce the pain and stiffness associated with water on the knee. Once your doctor determines the underlying cause of your water on the knee, appropriate treatment can begin.

Symptoms Causes Risk factors Complications Prevention

Signs and symptoms of water on the knee typically include:

  • Swelling. The flesh around your kneecap may puff up noticeably. This swelling is most apparent when you compare the affected knee to the normal one.
  • Stiffness. When your knee joint contains excess fluid, you may not be able to bend or straighten your leg completely.
  • Pain. Depending on the cause of the fluid buildup, the knee may be very painful — to the point that it's impossible to bear weight on it.

When to see a doctor

Seek prompt medical attention if:

  • Self-care measures or prescribed medications don't relieve the pain and swelling
  • One knee becomes red and feels warm to the touch as compared to your other knee

Water on the knee can be caused by many different types of problems, ranging from traumatic injuries to diseases and conditions.


Damage to any part of your knee can cause the painful buildup of excess joint fluid. Examples of traumatic injuries that cause fluid buildup in and around the knee joint are:

  • Broken bones
  • Meniscus tear
  • Ligament tear
  • Overuse injuries

Diseases and conditions

Underlying diseases and conditions that may produce fluid buildup in and around the knee joint include:

  • Osteoarthritis
  • Rheumatoid arthritis
  • Infection
  • Gout
  • Pseudogout
  • Bursitis
  • Cysts
  • Bleeding disorders
  • Tumors
  • Age. Water on the knee tends to happen more often in people older than age 55.
  • Sports participation. People who participate in sports that involve sudden changes of direction, such as basketball, are more likely to experience the types of knee injuries that cause water on the knee.
  • Obesity. Excess weight puts added stress on the knee joint, contributing to the wear-and-tear damage that may lead to water on the knee. This increases your risk of osteoarthritis, one of the more frequent causes of water on the knee.

If left untreated, water on the knee can severely limit your mobility. If the swelling is caused by an infection, it can destroy the joint.

Water on the knee is typically the result of a chronic health condition or traumatic injury. To prevent water on the knee, work with your doctor and other members of your health care team to manage the condition or traumatic injury that causes it. For example:

  • See your doctor regularly. See your doctor regularly if you have a chronic joint condition, such as osteoarthritis, rheumatoid arthritis or gout.
  • Follow through on your doctor's orders. Take the medications your doctor prescribes to treat the underlying disease or condition that causes water on the knee. If your doctor, physical therapist or sports trainer recommends you wear a knee brace because of a prior injury, be sure to follow through.
  • Strengthen your thigh muscles. If your thigh muscles are weak, your doctor may refer you to a physical therapist to learn how to strengthen these muscles to better support your knee.
  • Be gentle with your knees. If you're overweight and plan to start exercising as part of a weight-loss program, select an activity that doesn't place continuous weight-bearing stress on your knee joints — such as water aerobics or swimming.
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